Technical Field
The present disclosure relates to an organic light emitting display device and more particularly, to an organic light emitting display device with a reduced sub-pixel size, which is capable of displaying a high resolution image.
Related Technology
An organic light emitting display device, which is a self-luminous display device, does not require a separate light source in comparison to a liquid crystal display device, and is therefore made in a light weight and thin form. In addition, the organic light emitting display device is not only advantageous in terms of low power consumption due to its low voltage driving, but is also advantageous in terms of fast response speed, wide viewing angle and superior contrast ratio. For these reasons, the organic light emitting display device has been researched as a next generation display.
An organic light emitting display device includes a plurality of pixels for displaying an image. Each of the pixels includes a plurality of sub-pixels. The organic light emitting display device controls the brightness of the sub-pixel, thereby expressing various colors of the pixel, and realizing a full-color image.
The sub-pixel of the organic light emitting display device includes an organic light emitting diode (OLED) and a driving transistor providing a driving current to the organic light emitting diode. The brightness of the organic light emitting diode is determined by the amount of the driving current provided to the organic light emitting diode, and the amount of the driving current may be determined according to the electric potential difference between the gate electrode of the driving transistor and the second electrode and the threshold voltage of the driving transistor.
However, due to the characteristics of the manufacturing process, a deviation in terms of threshold voltage of the driving transistor may occur. For example, during the crystallization of the active layer of the driving transistor, the degree of the crystallization may vary with respect to each sub-pixel. In such case, the actual amount of the current provided to the organic light emitting diode may be different from the designed amount of the current. Thus, the brightness of the organic light emitting diode may be different from the desired brightness. Such deviation in terms of threshold voltage may cause irregularities of display that is referred as “Mura”.
A number of compensation circuits have been developed to compensate such deviation of the threshold voltage of the driving transistor. For example, a method, which initializes each electrode of the driving transistor to a certain voltage before the emission on the organic light emitting diode, and samples the threshold voltage of the driving transistor for compensating the threshold voltage, may be used. However, to realize such a compensation method, additional transistors and lines for initializing and sampling each electrode of the driving transistor are required. To give a more specific description with respect to this compensation method, FIG. 1 is referred and discussed below.
FIG. 1 is a schematic circuit diagram illustrating the sub-pixel of a related art organic light emitting display device. Referring to FIG. 1, the sub-pixel of the related art organic light emitting display device includes an organic light emitting diode (OLED), a driving transistor Tdr, a switching transistor Tsw, a first transistor T1, a second transistor T2, a third transistor T3, a fourth transistor T4 and a first capacitor C1. The sub-pixel of FIG. 1 includes six transistors and one capacitor. Thus, it may be referred to as a 6T1C structure.
In the 6T1C structure, the driving transistor Tdr provides a driving current to the organic light emitting diode (OLED). The first capacitor C1 is connected to the gate electrode of the driving transistor Tdr for maintaining a turn-on status of the driving transistor Tdr during an emission period. The first transistor T1 is turned-on based on a first scan voltage Vscan1 supplied from a first scan line 152, and configures a diode connection of the first electrode and the gate electrode of the driving transistor Tdr. The switching transistor Tsw is turned-on based on a second scan voltage Vscan2 supplied from a second scan line 153, and transfers the data voltage Vdata to the second electrode of the driving transistor Tdr. The second transistor T2 is turned-on based on a first emission control voltage Vem1 supplied from a first emission control line 154, and connects the second electrode of the driving transistor Tdr and the anode of the organic light emitting diode (OLED). The third transistor T3 is turned-on based on the first scan voltage Vscan1, and transfers an initialization voltage Vref supplied from an initialization line 155 to the anode of the organic light emitting diode (OLED). The fourth transistor T4 is turned-on based on a second emission voltage Vem2 supplied from a second emission control line 151, and transfers the high potential voltage Vdd to the first electrode of the driving transistor Tdr.
That is, the sub-pixel of the 6T1C structure includes the first transistor T1 and the fourth transistor T4 for initializing the gate electrode and the first electrode of the driving transistor Tdr to the high potential voltage Vdd. Further, the sub-pixel of the 6T1C structure includes the third transistor T3 and the second transistor T2 for initializing the second electrode of the driving transistor Tdr and the anode of the organic light emitting diode (OLED) to the initialization voltage Vref. Further, the sub-pixel of the 6T1C structure includes the third transistor T3, the second transistor T2, and the first transistor T1 for sampling the threshold voltage of the driving transistor Tdr. On the other hand, the first scan line 152, the first emission control line 154 and the second emission control line 151 are additionally required to independently control each of the first to fourth transistors according to the driving timing, and the initialization line 155 is required to supply the initialization voltage Vref.
As a result, the sub-pixel of the related art organic light emitting display device includes a driving transistor Tdr, a switching transistor Tsw, and a first capacitor C1 for emitting the organic light emitting diode (OLED) and may include additional compensation transistors. Further, additional lines are additionally required for independently controlling each of the compensation transistors.
As the structure of the sub-pixel becomes more complicated, however, the size of the sub-pixel tends to be larger. Thus, the number of the sub-pixels arranged within a unit area tends to be reduced. Accordingly, this is a problem in that the resolution of the organic light emitting display device may be reduced and a manufacturing cost of the organic light emitting display device can be increased.
In addition, this is a problem in that due to the arrangement of the additional lines, a parasitic capacitance between the lines can be generated. Thus, it is a problem that an interference between the signals for driving the organic light emitting display device can occur due to a coupling by the parasitic capacitance.
Accordingly, there is a need for an improved display device in which the development of a circuit layout not only can compensate the deviation of the threshold voltage of the driving transistor but can also simplify the circuit layout and reduce the number of various lines.